1. Field of the Invention
This invention relates generally to refrigerators, and more particularly, to an improved thermostat mounting system for automatic defrost refrigerators and the like.
2. Description of Background Art
Conventional frostless or automatic defrost type refrigerator/freezers utilize an electric resistance heater which is energized to melt away frost that accumulates on the coils of an evaporator. The heater may be controllably energized by, for example, a frost sensor or a timer. Once the frost has melted, it is necessary to de-energize the heater. A thermostat, such as a bimetal sensor, is typically utilized for de-energizing the heater according to the sensed temperature. Therefore, the thermostat should be positioned so as to insure that all or most of the frost has been melted away prior to de-energizing the heater.
One location for mounting a defrost thermostat is on one of the coils of the evaporator. A mounting bracket for such an installation is illustrated in Place U.S. Pat. No. 4,297,668. However, due to the coil being of curved cross section there is a limited surface contact area between the thermostat and the coil. Also, due to varying amounts of refrigerant at different positions in the evaporator coil, and the fact that the heater may not melt the frost uniformly across the coil, problems result from the use of such a mounting system. Particularly, while frost may have melted at the particular location of the thermostat, frost may remain elsewhere.
A desirable location for the defrost thermostat is to have it mounted above the evaporator. Refrigerators constructed with plastic liners typically use a metal protective liner, or heat shield, separating the evaporator from the liner. The heat shield is in heat transfer association with the evaporator. It has been proposed that mounting the thermostat to the heat shield, above the evaporator, provides a more representative temperature measurement than having the thermostat mounted to the evaporator coil.
In order for a thermostat mounted to the metal plate to function reliably, the thermostat should be maintained in facial contact with the heat shield. Moreover, it is desirable that installation be simple and achievable at low cost. Also the thermostat should be easily replaceable. Additionally, it is desirable that fasteners, such as screws, are not utilized which would penetrate the plastic liner.
The present invention overcomes the above problems of the prior art refrigerators/freezers in a novel and simple manner.